Organic photoreceptors (hereinafter also referred to simply as “photoreceptors”) having a surface layer made of a cured resin as a protective layer have been widely used. The cured resin constituting the surface layer is usually produced by polymerization of a polymerizable compound by heat, electron beam, ultraviolet rays, or the like.
The surface layer is usually formed by applying a coating liquid in which a curable, polymerizable compound(s) for forming a cured resin, a polymerization initiator and other optional components are dissolved or dispersed in a suitable solvent, to the surface of an organic photosensitive layer formed on a conductive support, and curing the obtained coating film to give a cured resin.
When the curing process is performed by a radical polymerization reaction with ultraviolet irradiation to undergo polymerization of a radical polymerizable compound, the radical polymerization reaction has been known to be inhibited by oxygen in the air, called oxygen inhibition. This oxygen inhibition hinders the radical polymerization reaction to provide a surface layer which generally has low hardness and also has a large variation in hardness. This leads to uneven abrasion of the surface of a photoreceptor after long time use and finally causes in-plane image density unevenness.
To suppress this oxygen inhibition, there have been proposed curing processes under inert atmosphere such as nitrogen and addition of a chain transfer agent containing a thiol compound to a coating liquid (see, for example, Patent Literature 1).
However, the radical polymerization under inert atmosphere and the use of a chain transfer agent containing a thiol compound as described above failed to sufficiently prevent uneven abrasion of the surface of a photoreceptor.